WBCS.LIVE practice question

A can complete a piece of work in 15 days, and B can complete it in 20 days. If they work together on it for exactly 4 days, what exact fraction of the work is still left to be completed?

Solve this multiple-choice question and check the correct answer with its explanation below.

Answer options

  1. 8/15
  2. 7/15
  3. 1/4
  4. 1/3

Correct answer and explanation

Correct answer: 8/15

Explanation: ✅ Correct Answer: A) 8/15 📚 Explanation: A's 1-day work is 1/15, and B's is 1/20. Their combined 1-day work is (1 ÷ 15) + (1 ÷ 20) = (4 + 3) ÷ 60 = 7 ÷ 60. Since they work together for 4 days, the total work completed is 4 × (7 ÷ 60) = 28 ÷ 60, which simplifies to 7 ÷ 15. The fraction of the work left is 1 - (7 ÷ 15), which equals 8/15.